Ouch! A shark bit your arm

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Swimmer bitten by great white shark

"I could feel the vibration of this entire shark gnawing into my skin," he said. "You could feel the whole body shaking as it's digging into my torso."

The burning sensation of the bite is hard to forget.

"The bite mark's like a jellyfish sting that just keeps penetrating deeper and deeper into the bone," Robles said. "It was terrifying."

He grabbed the shark's nose with his hand and tried to pry him off. Fortunately, the shark left on his own and darted away.

A witness's cell phone video posted by CNN affiliate KTLA showed Robles screaming loudly as fellow swimmers tried to help him to shore. Witnesses on the pier screamed that the shark was still close by.

Police closed down the Manhattan Beach Pier, and it will remain closed until Tuesday.

While shark attacks are rare, they have increased at a steady rate since 1900 "with each decade having more attacks than the previous," according to the International Shark Attack File based in Gainesville, Florida.

But the ISAF says there were 72 unprovoked shark attacks on humans in 2013 -- the lowest number of global attacks since 2009, when 67 attacks occurred.

The group emphasized that an increasing number of shark attacks doesn't mean the rate of attacks is increasing. ISAF research shows people are spending more time at sea, which increases the interactions between humans and sharks.

Robles said even though he thought he might be dying, his survival instincts kicked in.

"My life was just a half a second from ending, and I had to fight for my life," he said.

Just before the attack, Robles said he was planning another long-distance swim. But now he says he might never swim in the open water again.